In recent years, in millimeter-wave wireless communication using a 60 GHz band, a plurality of wireless communication standards have been developed and studied. Main wireless local area network (LAN)/wireless personal area network (PAN) standards which do not require a license include wireless gigabit (WiGig), IEEE 802.15.3c, Wireless high definition (HD), and ECMA-387. The development of the IEEE 802.11ad standard is also in progress.
In each standard, a plurality of radio systems (for example, a single carrier system and an orthogonal frequency division multiplexing (OFDM) system) according to a target application coexist.
The systems respectively corresponding to a plurality of wireless communication standards coexist, and a plurality of wireless systems also coexist in each of the systems. When millimeter-wave wireless communication comes into wide use, it is assumed that there are many situations in which a plurality of different wireless systems are used proximately. For this reason, the systems use different frequency channels, thereby making it possible to perform communication simultaneously in the same space.
However, because the number of frequency channels available in the 60 GHz band is limited to three to four channels, when millimeter-wave wireless communication comes into wide use, it is expected that a plurality of different systems use the same frequency channel. As a result, inter-system interference occurs, and there is concern that communication performance in each system is degraded.
In order to avoid the interference, first, it is necessary to detect an interference signal from a different system with respect to a target system. Heretofore, as a signal detection method, carrier sense by power (hereinafter, simply referred to as “carrier sense”) is widely used. Carrier sense is a method which detects power to detect a signal.
Specifically, in carrier sense, power of a received signal is measured, and when the measured power value exceeds a predetermined threshold, it is recognized that a signal is detected. Carrier sense has a feature that a signal can be detected regardless of the types of systems.
As carrier sense, for example, technology disclosed in Patent Literature (hereinafter, abbreviated as “PTL”) 1 is known. PTL 1 proposes a method in which: in carrier sense of clear channel assessment (CCA) of IEEE 802.11, for example, if power (level) exceeds a predetermined threshold, it is determined to be a busy state representing that a transmission medium is in use; even if power does not exceed the predetermined threshold, the state transitions to a pending state in which determination on whether or not the transmission medium is in use is in progress; and if a preamble is detected in the pending state, it is determined to be the busy state. Accordingly, the signal of power which does not exceed the predetermined threshold can also be detected.